If it's a 2010 close-out model - there is a great price on them right now. These have the sachs fork and sachs shock. The sachs fork is what is used when they install ttx cartridges in the "nambotin replica" gasgas - ohlns part number fggg 1182.
I would probably sell the TTX cartridges you have and buy the ones that are made to fit in the sachs fork. Your CR TTX cartridges are very desire-able and you are coming into tax refund season where a little extra cash is floating around the economy - so you should be able to "move them".
I would budget for a revalve for off-road work as the ohlins TTX come valved for MX work.
The sachs shock that will come on the 2010 is of very good quality - like most euro suspension - the materials used are higher quality than their japanese counterparts. The shock has had a couple of small issues (piston ring tension and a check ball tolerance that are easily fixed - see
www.lt-racing.com for details) - given that, the sachs is a very high quality shock with an alloy steel body and more reliable piston reservoir like the ohlins. The steel body yields less fade when hot and the oil stays cleaner longer providing longer service intervals. So, if you are on a budget you could sell the rear ttx shock as well and use the money towards upgrades on the new bike.
Another factor will be the future resale value of your new GasGas - in that regard - resale will be higher if you go with ttx cartridges in the sachs fork and hopefully getting the ttx rear shock to fit on the bike.
If you are tight on cash - you could go TTX cartridges on the front and use the sachs rear shock - it's a very, very good shock.
Jeff