Being a very light sailor, here is my experience about all that:
- First, I have a similar problem:
. I most of the time start planing before the others,
and therefore I'm rather quick in marginal conditions.
. When there is more wind, I must take a very small sail and
I'm very slow.
- My guess is that being light is a drawback for pure speed
(I think the record man for speed is about 220lb)
I also think that height does not change anything.
But level of sailing has a big importance.
- I don't agree with statement like 25 lb = 0.5 m2 of sail,
because it depends on the wind.
One should compare sail sizes proportionally.
6.0 / 7.5 = 0.8
4.0 / 5.0 = 0.8
So according to me, a difference of 1.5 m2 in 7.5 conditions
is the same as a difference of 1.0 m2 in 5.0 conditions.
- 5.0 for 135lb = 6.5 for 180lb seems a little small to me.
I would rather say that:
5.5 for 135lb = 6.5 for 180lb, but ...
... it's really a hassle to be overpowered, so if you feel good
that way, don't change!
- My opinion is also that the E-Rock has a rather old design now, even
older than the A-Rock, and is really not a fast board.
For instance, the Bic Adagio although rather old, has
a better shape for slalom than the E-Rock.
- I used to sail a wave board (F2-Starlit) in slalom conditions,
and I bought a slalom board (F2 Sputnik 275). It makes a huge
difference in speed.
I also have learnt to sheet in better, and have more powerfull
sails since then.
- And finally, it does not matter so much to be the fastest.
It's much more fun to duck jibe around a guy that just passed you
and crashed in a jibe!
(I just learnt to duck jibe this summer, after all it's not
that hard -- got a rate of success of 1/2 after 3 days of practice
on flat water with a 5.5m2.
Those who can jibe and have never dared to try should
go for it. It's really fun, and actually not harder than carve jibe.
To make it, one should be planing, and flip the sail very early.
By the way, thank you to all who responded to my question
about choosing a 6.5 sail. I finally bought a NP V8 and I love it.
It's powerfull and handles guts rather well.