re 620. Yes it gives you the new novelty stats although from what I gather, nobody knows what to do with them. I'm looking forward to the wifi connectivity and having 4 data fields on one screen. The HRM monitor is meant to be very accurate too.
The wifi / bluetooth connection is excellent. Talking of Novelty stats, I've had the 620 since November. The VO2 / Race Time predictor is good for a laugh. Mine has settled at:
VO2Max = 63, Race Time Predictors:
5K: 16:19 10K: 33:53 HM: 1:14:50 Mara: 2:36:33
I will be sure to shout about those times when I get them
If you are going to do it, learn through practice outside of marathon training. As Millsy says, don't dive into it. I used last spring/summer to introduce speed work to my running. When it came to the next Marathon training plan I knew what I was doing in terms of organising the sessions, where I would do it, what type of warm up / cool down is needed etc. I wouldn't want to take this up in the midst of marathon training