Hi HouseyMouse,
All of those schools have very good reputations and are hugely oversubscribed. To get a place you would need to move extremely close to one of them. No point being in the middle thinking you'll get one or the other, the likelihood is that you will get none of your choices and be allocated a much less well regarded school far further away. The school places situation is getting worse, year on year. My dd1 got in in 2009 but we would have been too far away for her to have got a place for 2010 or 2011. Luckily dd2 has a sibling place for this year.
Henleaze this year had 66 siblings so only 24 spaces for new families and the distance was three hundred and something metres, as the crow flies. Elmlea took up to about 600m away for 90 spaces (51 siblings) and Westbury on Trym I think about 400m for 60 spaces again with more than half being siblings. The new primary at Brecon Rd (formerly St Ursula's) may take the pressure off places slightly for 2012, but as the school is not yet open, no-one knows how good it will be.
The schools are definitely not the same as each other, so it would be worth you looking around to see which you prefer. Westbury is smaller, but all through from 4-11. Henleaze and Elmlea are 90 intakes but separate infant and Juniors. Elmlea keeps their 3 classes of 30 quite separate from each other apart from outside playtime. Westbury combines their 2 classes for reading groups, maths groups etc so it sometimes feels more like one big class of 60. Don't know so much about Henleaze apart from there is a new head at the Infants. My friend with children there isn't very impressed with the new infant head, however is full of praise for the Junior Head.
Bishop Rd, Sefton Park, Westbury Park are, I would say, equally well regarded, but no easier to get into and I don't personally know much about them. Will happily answer any other queries you may have, as it is a bit of a minefield!