You seemed to used 6k a few times in the Spa vid, but I understand where you are coming from with Rovers (unless bonkers money engines, like they use in MGBV8's now with split plane cranks they are all torque and not big power - those guys rev to 7k+ but they do not seem to be reliable, they do get 400bhp from a 3.9 - 4 litre, but then if they then destroy themselves what is the point!). Imagine one of those in your car.
I had similar experience with 2x 5ltr ones in my Chimaera’s in the early 2000’s, only made about 280bhp but very good torque (advertised as 320bhp and 320 ft/lbs which always used to really annoy me), they felt like they were just about to grenade themselves at the red line. Mind the larger RV8 are made just on stroking them as a pretty compact little engine, so a 5litre revving at 6 is a lot different to a 4.0 doing the same. Had a mate back I the day (mid 2000’s) who had a 5.5 one from V8 Developments in the UK, made about 340bhp but well over 400ft/lbs. Mind I’d given up on them and sold my second RV8 in 2nd Chim after cam went (and repaired at <25k miles!) and did the first LS conversion of a TVR in the UK (https://engineswapdepot.com/?p=11916), the thing was an absolute Monster (with a real 400bhp & torque).
Your car must have long gears Chris and obviously pulls crazy G’s in the corners with the steam rollers tyres (where most of the laptime must be coming from). Make my current TVR look silly on 225/60x15’s, wobbling about! Power is utterly bonkers, but when it don’t go round corners (well relative to my TR6!), but working on this….
I’ll likely stick with a lowish 6.3ish change point in the TR4 even though I could probably run a lot higher with the good stuff in the engine now i.e. 67-6800+ (and did last year at Mallory in its first full 40 min race with no issues - well through the kink I'd have lost too much time changing up then down!).
I feel for you Dave. Doing Angelsey?