I have ordered Whiplash TWag Elite replacement cables for all my dynamic Sennheisers (HD600/650/800), with the biggest--and I mean enormous--improvement experienced on the HD600/650s. Wrote up a review on that (Duel of the Xes) in my sig block.
Since the review I have upgraded my amps and ICs using the same cables so the synergy is even better. I had another Head-Fi'er over to visit and when he heard them for the first time (after experiencing them in stock form) his jaw dropped. He said these cables have completely elevated the sound signature of the cans to the point were they could be compared to reference cans costing 2-3 times their price in terms of SQ, if not build quality and comfort.
But these cables retail around $425 depending on termination and length. I suppose you get what you pay for in this case.
So, you could basically drop the price of a T1 on your HD650s+cable, OR you could just get the T1.