I've got an SX trail great all round Bike, but if u really want to focus on downhill, a big bike is more fun and much easier. This year at Ft William I took my Cove STD with Totems on it (big freeride bike), rather than the SX trail and the difference was staggering..way more fun. The SX Trail is superb for relatively smooth stuff and fantastic on boards/shore but the bigger bikes are better on gnarly rock gardens and when it gets steep.
SX Trail climbs o.k and is great going down too. I enjoy using mine on the Scottish Highland trails & 7 Staines
For DH..Maybee a Spec Big hit(they are great value big bike) or a Giant Reign…both VERY heavy and you will need to push uphill unless you are superman! I would agree that if you can only have 1 bike & like mixing DH with trail riding, the SX trail is probably best.