The focal length doesn't make much difference. There will be things that are too big or too small, no matter which you choose.
IMHO, the biggest difference in focal ratios would boil down to needing a coma corrector for f/4 and wanting one for the f/5. The difference in
exposure time is the same as it would be for
lenses of the same focal ratios. ie. about 60% longer. In reality, that doesn't matter either because no matter what, you'll always want more.
The most important thing to ask/check is that you can achieve focus with a DSLR. Most standard newtonians don't allow you to wind the focuser in far enough for photography. Some are sold as "Astrographs" (designed for photography) which are suitable. Others may require a lower profile focuser and/or moving the main mirror up the tube by an inch or two.
Also keep an eye on your weight budget too.
Steve.