garmin 500 or sigma rox 9.0 or?

I want to upgrade my pretty basic cateye computer that will be moved on my track bike and want to upgrade for something which would allow me to analyze the data such as speed (maximum, ave etc), cadence (maximum, current, ave), heart rate (all functions + preferably showing when I'm changing through zones), alitude and slope would be an advantage but it's not necessary as I don't think even the best computer on the market would do that properly.
I was thinking of garmin 500 with cadence and HR which costs around £250, and that's quite expensive for me, but I could stretch. I have also seen Sigma Rox 9.0 and has good compability with two bikes (training + racing). It is easy to swap over the garmin between two bikes too? Sigma is way cheaper but doesn't have gps, which is btw. cr@p as far I as know from various reviews - it only tracks.
Which should I go for? Anyone can share experience with any of these two? Are there any other quality or cheaper alternatives ?
and well, garmin would allow me to use a powermeter of any kind, if I decide to get one in future...
I was thinking of garmin 500 with cadence and HR which costs around £250, and that's quite expensive for me, but I could stretch. I have also seen Sigma Rox 9.0 and has good compability with two bikes (training + racing). It is easy to swap over the garmin between two bikes too? Sigma is way cheaper but doesn't have gps, which is btw. cr@p as far I as know from various reviews - it only tracks.
Which should I go for? Anyone can share experience with any of these two? Are there any other quality or cheaper alternatives ?

and well, garmin would allow me to use a powermeter of any kind, if I decide to get one in future...
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Anyway, I would appreciate all the reviews.
PS check out handtec they are good to deal with and cheap.
http://www.handtec.co.uk/product.php/2336/garmin-edge-500
http://www.pinkbike.com/photo/2236156/
http://www.pinkbike.com/photo/2236165/
There is one highly annoying feature of the Sigma, too, which is that it does not always record data - you need to actually remember to ask it to log data every time, otherwise you can find that you have had live data all ride but captured none.
The GPS on the Garmin is now invaluable to me - and I thought that it might be a gimmick.
So, my view, after more than a year with each device, is a big vote for the Garmin, unless you are planning on regular 24-hour TTs, in which case the battery life will be too short, so the ROX would be better.
small steps
great review of both, most useful features. I'm not planning anything longer than 8h I think, so I would be fine with charging the battery. Can you replace the battery during the ride if you have another one? The garmin would also look nicer on my bike
As for charging the unit, ive never had to charge mine after just one ride, id say i get about 200-250mile out of a charge. And you cant change the battery its built in.
You'll enjoy using it, the worst bit is setting it all up. The Garmin Connect site is a pretty good tool too.
RichB.
09 Canyon Ultimate CF for the Road.
2011 Carbon Spesh Stumpy FSR.