While 7ft can be a little bit long to be comfortable, I do need the rods to be that length to be able to reach around both ends of the kayak which is vital I reckon.

As Hermit mentioned there is two schools of though on this issue.
I'm of the other side..
I've got three berkley's that I use for SPs
a 6', 6-10kg (spin)
a 5'10" 6;8kg (baitcaster)
and a 5'8" 4-6kg (baitcaster)
Getting around the bow is something I rarely need to do, even with a 7' rod, try getting the line around the bow when the rod is loaded up...it's not that easy anyway!
As for casting distance, I've had days where I've thrown the whole 100yd top shot off the spool and been onto the mono backing(wind assisted) but after doing a bit of refining I find I don't generally need to cast to far anymore. If the fish are showing on the sounder below me I target them and 9-10 times do pretty well. I rarely cast further than 30m these days and thats in the wash up against the rocks.
The shorter rods, especially, in the stiff carbon jobbies are heaps easier to land a fish without the worry of tip loading, something im7 graphite hates!
But in saying all of that, it's like anything on a yak, it depends on how YOU fish and what YOUR use to.
One thing I would suggest is if you get a shorter rod, make sure there is enough of a butt section on it so you can put the hurt on the fish without feeling cramped up with your arms bent right up.
My 2 cents anyways...