I’ve not heard them side by side for comparison but am fairly familiar with the range, it’s still the 600 just an updated version. Of course there will be improvements on the newer model but it’s not going to be night and day. You may just want something that looks a bit more up to date and if that’s your motivation then fine but I wouldn’t consider it a huge upgrade. As I said if it were me I’d either stick with what you’ve got wait till you can afford to make a purchase which is a definite upgrade, not simply an updated version of what you already have. The CM9’s for example will give you that same house sound but will be that bit more refined, the CMs are known for being very detailed speakers and should prove a hit for someone coming form the 600 series. The CM9 however are quite a bit more expensive than the 600 series, if you can live with a bit less bass the CM8 are a slimmer version, again a 3 way floor stander but the profile and footprint is less and the drive units smaller. They have many fans though and were once on my shortlist as a possible speaker upgrade.
I suppose it depends on what you’re trying to achieve, as if life unless you’ve got an unlimited budget there’s going to be a compromise, if you want speakers the same size but of higher quality you need to pay for it. You could of course go for smaller higher quality speakers, which would be closer in price. I actually think the CM8s could be a good middle ground. They retail at £1,250 but I have heard of people getting good deals on them right now for around £1k. If you went smaller you could look at the CM1’s and the CM5’s as well as others brands such as a used pair of PMC DB1is.
Also have a look at the XTZ speakers, the 99.36 floorstanders and the smaller stand mount version the 99.26s. While I’m not convinced by the XTZ electronics their speakers have a great following on various forums and by all account punch well above their weight in terms of price performance. The 99.26s were group tested and did favourably against the B&W 805S (not the newer Diamond version) in one review which speaks volumes.