Lots of very interesting observations, thanks everyone. I guess for grain I already have the 1600 in the F3. And I do like grain sometimes. I've used HP5 and FP4 in 120 format where the grain in HP5 isn't an issue when enlarged pretty big. I think I need to try FP4 in 35mm and see how I get on with it. I'm usually trying to maximise depth of field, so the slow down in shutter speed may be an issue. I have thought about a move to a different t-grain 400 film but thought I'd mess around with what I know a little about first before a total change, and HP5 in XTOL is what I know best.
I'm not a fan of T-grain technology. I don't think it is always possible to put all the grains in the same direction and it seems unatural somehow. I can't really describe why, I just don't like it.
FP4+ for greater expansion of the film's density range.
And for being able to use lenses without shutters easier in bright light.
If you are doing landscapes or other types of photography in which the subject is static, I'd highly recommend you use a tripod. TRIPOD. Then you can use a slower film like FP4+. And as some others have already said, FP4+ is an absolutely wonderful film in every way. Probably my all time favourite film if I had to pick one. If you want finer grain than FP4+, you could also try the tabular grain films such as Delta 100, Acros or TMX. Alternatively you could just use TMY-2 for everything (it is as fine grained than Delta 100).
I love my FP4 and if you really want to, you can push it to 200 without too much grain. I develop it in Rodinal to give a bit of bite for sharpness and the slow speed doesn't make it too grainy (HP5 in Rodinal is terribly grainy for me). That said, I use Tri-X for walking around, as it is more flexible when moving indoors. If a tripod is too much hassle, go with the monopod.
I switched too FP4 a little while back as my primary 35mm film and I rarely miss the faster speed, of course I'm normally an f/2 to f/4 and be there type shooter.
Like the OP I find the grain from 35mm HP5 regularly gets in the way when printed larger than 8x10.
Delta 400 is between the two.
You don't need a tripod to steady a camera there are several other methods.
o lean against a wall
o use a beanbag on a horizontal surface
o use an easy to carry monopod
o use a 1/4 inch coarse thread eyelet screw in tropod hole and a length of cord under your foot to steady camera
o tuck your elbows into your body and hold your breath