Interesting comparison gear ratios. If I translate that to shifts at Thunderhill, for example, we would need a shift to 5th on the front straight, then a downshift through T1 to fourth. We rarely get to 5th in an SRF3 without a tail-wind/draft. Apex speed is 95-100, so 4th gear is the same. Entry to two would be between mid to upper 70's mph, so 3rd gear.
This is one area where we "debate' between staying in third and going up to 4th in the 3, since hitting over 90 is likely, so the Gen 4 will likely require an upshift to 4th before getting to T3. Probably a wash, so I'll call it even for the required up-shift and subsequent downshift to 3rd into T3. T3 to the Crow's nest is from ~70 mph to low 80 mph, so that all within the 3rd gear range.
Gear-wise, the Crow's Nest would, technically, be a 2nd gear corner (apex high 40's mph), but since it's immediately downhill, most leave it in 3rd. Entry to T6 is in the mid-80mph range (ideally), so still in 3rd. Shift to 4th would be slightly earlier, carrying you to T9.
Interestingly, T9 will be right on the edge of the SRF4 limit, but under most conditions it looks like the RPM limiter won't be hit, so a downshift to 3rd takes you to an upshift to 4th before T10. Apex speed in T10 is would require a downshift to 3rd.
T11, with an apex speed in the low to mid-50's, is one of those six-of-one corners where 2nd gear is tempting, but most will live in 3rd gear. This is one place where an LSD might be helpful since it's an up-hill left (1.5g), followed by an immediate flatter right / left. Using 2nd gear would require an upshift near the apex of T12, so it's TBD if the 4 has an advantage (and how much).
Up to 4th down the backstraight to the T14/15 turn back to the front straight. Maxing out at under 110mph, that sets up another possibility to use 2nd gear as the apex speed is in the upper 50mph range. Most just leave it in 3rd. Back to the front stretch to finish the lap, with an upshift to 4th shortly after entering the straight.
Looks like, at a minimum, an upshift to 5th will be required into T1 (and subsequent downshift to 4th). T2 to T3 will require an up-shift to 4th and downshift to 3rd entering T3. There may be use for 2nd gear in the three areas of the track, but likely not required (or helpful without LSD. The 4th gear ratio will likely make the most difference in overall performance. I suspect the sequential shifting will help on up-shift times for some, but on a two gear track, with 4-5 upshifts, I suspect that won't make a large difference.
On the weight I think a nice round number like 1,600 would work for SRF4... (that should get things going!)... (and take SRF3 down to 1540...)