I would go table, arm and cartridge in descending order of importance. The relative place of arm and table can be debated but both will have more influence than the cartridge in that there is no way that the best cartridge can perform with inferior table and arm. The 300 is quite a good arm, make sure that it not a sideways move. You don't mention your phono stage, you might get more improvement for your money here depending on what you have now.
tonearm upgrade, how far up the food chain?
I currently use a Rega RB 300 upgraded with the Origin Live structural mod (i.e. counterweight) and Incognito rewire. It's on a Thorens TD-850, Grado Statement Reference cartridge. Based on comments here on the Gon, many seem to feel that upgrading the arm should come before the cartridge or table, under the circumstances. How far up the ladder do I have to climb to get a noticeable improvement? And, do arms (that is, their bearings) really wear out, or their performance decline, with normal use? considering midlevel Origin Live arms, given the Rega mount. thanks in advance for suggestions.