My layout is designed for 8-coach trains. It has lower and upper levels on one side, to accomodate hidden storage sidings below and a scenic run above. I ran some tests with Hornby Bulleids, King Arthurs, standard 4s and 5s etc. and found I needed a gradient no steeper than 1 in 70 for these. The King Arthurs would only take 8 Bachmann MK1s up this gradient after the coaches' weights had been removed - otherwise it was only 6. The gradients are all on 36-inch radius curves also, which doesn't help.
No problems with diesels I found - Heljan class 33 would take 12 without blinking. Likewise Bachmann 9Fs.
I'd suggest you do some tests with your intended locos and coaches and see what the results are, taking into account curves as well. I also tested both through running as well as starting from the bottom of the gradient and half-way up. Some locos would reach the top if given a good run at it, but wouldn't start on the gradient.
No problems with diesels I found - Heljan class 33 would take 12 without blinking. Likewise Bachmann 9Fs.
I'd suggest you do some tests with your intended locos and coaches and see what the results are, taking into account curves as well. I also tested both through running as well as starting from the bottom of the gradient and half-way up. Some locos would reach the top if given a good run at it, but wouldn't start on the gradient.