As suggested above, search this forum of recent, and see globalflyfishers leadercalc.
But here’s my two penneth worth as well……
In my humble opinion, going from a 7wt? line straight onto such a long 8lb butt section wouldn’t really achieve the object of transferring the energy from the flyline down through the leader to the fly. I would imagine its better than completely straight through, but not much.
I’ve been dabbling with rolling my own this season and am happy so far with the results, and my first advice would be to forget about breaking strains of line and concentrate on diameters. If you want to do it properly and think you might stick with the hand tied method, at least for a couple of dozen leaders, get yourself a range of lines from say 0.5 – 0.6mm (or 60-70% the diameter of the end of your flyline) down through to 0.2mm, in steps of about 0.05mm (see my basic make up below). It’ll cost £30-40 which might seem like a lot of money to shell out all at one once, but with knotless leaders costing about £3 a piece, you only need make/use a dozen or so and you’ve got your money back, whats more, from a set of 300m spools you could get about 500 leaders easily (8pence per leader by my reckoning!)
The basic 11’ one I’ve started with as a benchmark for refinement, which to be honest is working quite well as it is, starts at 0.52mm (25lb - about 70% the dia of the end of my DT4F), reducing in 7 steps down to a 0.12mm (1.8kg stroft) tippet, its roughly made up as follows:-
22” 0.52, 20” 0.45, 20” 0.40, 15” 0.35, 10” 0.30, 9” 0.25, 9” 0.20, 24” 0.12 Tippet. As a rule of thumb each section is roughly .05mm the diameter of the preceding one, with each getting progressively shorter towards the tippet section. I based it as near as damnit to a standard 11’ dryfly leader on leadercalc and altered it within reason to suit the diameters that I have.
When you’ve made one, straighten it out, then flick it out across the floor to see what it does, its fairly easy to get a ‘feel’ for if it’ll turnover.
Rover