G'day James, ... could you do me a favour and edit your initial post title to 'Defender of the Faith & Aid Grades' (so I can easily access this info again when required; thanks) ...
>I thought A2 was bordering on dangerous/scary (in terms of fall potential etc).
Climbing Big Walls (Strassman) says;~
A1 = A perfect crack that was neither strenuous nor reachy and awkward.
A2 = A good crack but awkward and strenuous.
A3 = Would require more difficult placements that couldn't be counted on to sustain the impact of a fall.
A4 = One to three aid placements which would hold bodyweight only.
A5 = More of A4 in a row; 2 placements equally weighted necessary to hold bodyweight. Around 1974 this was amended to include a potential 60' (approx 18m) fall potential.
Big Walls (Long / Middendorf) says;~
A1 = Placement normally easy to set, solid and capable of holding a good-sized fall. A straightforward and secure piece of work.
Tricky A1 = Bombproof placements are obtainable but you need experience and ingenuity to secure them.
A2 =Creaky non-optimal placements requiring some savvy and tinkering to set. Generally solid though not ideal, and probably adequate to arrest moderate falls.
A3 = 'Real' climbing / advanced work. Flaky incipient cracks, micro pitons, hooks, copperheads, ... the whole panoply of aid gimmicks, pushed close to their limits. Good enough for bodyweight but little more. Will not arrest a fall and marginal going at best.
A4 = So marginal may pop when tested. Can never hold a fall. Stretches of placements that would unzipper in a fall.
A5 = Danger. If one placement goes, they all go and physical harm is assured.
Post 1980 'New Wave' Ratings;
A0 = Pulling on gear but nil ettriers required (ie "french-free").
A1 = Easy placements, straightforward, solid and no risk of pulling out. Aiders (etts) generally required. Fast and simple for 'clean aid' but 'clean' usually requires more time and savvy.
A2 = Moderate placements generally solid, but possibly awkward and strenuous. Maybe a tenuous placement or two above good pro with no danger involved in a fall .
A2+ = Several tenuous placements above good pro with 30' (10m) fall potential and minimal danger of hitting anything. Route-finding abilities may be required.
A3 = Hard aid. Testing methods required. Many tenuous placements in a row. Generally solid placements which could hold a fall can be found within the pitch. Long fall potential (50' / 18m ie 6 to 8 placements ripping), but generally safe from serious peril. Several hours required for leading the pitch due to complexity of placements.
A3+ = Dangerous fall potential. Potential to get hurt if good judgement is not exercised. Tenuous placements after long stretches of bodyweight only placements. Time required to lead a pitch generally exceeds 3 hours for experienced aid climbers.
A4 = Serious. Lots of jeopardy. 60'-100' (20m-30m) fall potential common with uncertain landings far below.
A4+ = More serious than A4 with leads taking many hours to complete requiring leader to suffer long periods of uncertainty and fear. Requires ballet-like efficiency of movement in order to not upset tenuous integrity of marginal placements.
A5 = Extreme. Nothing trustworthy of catching a fall for the entire pitch. No bolts or enhancement holes. Dangerous leading with death fall potential.
A6 = (Theoretical grade) A5 climbing with marginal belays that will not hold a fall, such that if the leader pings, its into the beyond for the whole team.
Clean aid = 'A' grades but 'A' is replaced by 'C', (eg C1, C2 etc).
Comment / Discussion:
Historically A5 = the most difficult thing going / cutting edge aid; ... and to add A6 etc renders this grading system useless (paraphrased Long/Middendorf).
I have noticed A6 and A7 'mountaineerig walls' more recently written up.
Australia uses the M1 to M8 system (for historically equating to A1 to A5).
In my opinion A5/A5+ = M8 which equates with the historical perspective.
... on that basis A6 would be = to M9 and presumably A7 = M10, though its quirky fitting the +/- USA nuances into our 'straight' system.
The A6 / A7 stuff appears to be reserved for remote expedition style walling, and since we don't have any of that in Australia (Antarctic perhaps?), we may not see these grades till something revolutionary happens, or Australians put up hard new routes on Baffin or Patagonia, Pakistan etc. If Aussies wave that flag, its likely that they will simply give the grade as A6, A7 etc being overseas and all ...
>What is your opinion of the aid grade of Defender? The guide says M5... is this A2+??
IMO Yes, in the 'old' scale, and probably* also in the present system.
*I have not led this climb (yet) as its still on my 'to do' list. I have abseiled / jumared it though, and it looks relatively straightforward to me.
To stir the pot I'd call it C5 !!
Edit: Thanks for the title edit !