Increasing size without additional slippage? Then, all oil-related contracts, both in Nymex and ICE.
Higher diversification and a smoother equity curve? Try FX majors (with the possible exception of JPY) and non-limit commodities (particularly HG - copper).
thanks for the reply's, yes mainly for slippage, and more trading opportunities, plus i want to see how other markets that are somewhat similar behave with my style