A 4 carat princess cut should look huge, and for the budget, you should be able to find one with good color and no noticeable flaws (to the untrained eye). An emerald or asscher cut will cost more (or be smaller) and may not look quite as large because of the chamfered edges, but they will have a much better sparkle due to more facets.
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2011 370Z 6MT Sport Gun Metallic | ARC | CJM | Ecutek | FI | Fujimura | R2C | SPL | Stillen | TWM | Z1 | ZSpeed | |