I'll just bet ya that if you spend more time and attention on the antenna choice - rather than the amplifier choice - then you will get out better, spend less money, and be happier with the final results.
A 4 ft antenna just isn't a decent choice no matter who makes it - IMO. How is it that I can talk all over the US with just 35 watts? ANS: because when skip conditions are present, the 6 1/2 ft Sirio Z-180 antenna is really pulling the load. Fairly wide banded too. Short antennas generally have very narrow bandwidths. The SilverLoad isn't the worst 4 ft antenna out there; but you could do so much better than that choice - to say the least.
Howabout a Predator 10k, a Sirio5000, or a 1/4 wave/108 inch steel whip and just a 350 watt amp? Where and how you mount that antenna will also make quite a difference - too. Even a Wilson 5000 mag mount antenna on the center of the roof is doable, cost effective, and will work quite fine with a 350 watt amp. Now; that is clearly a better option. The best results are found in the details; not necessarily the amount of money you spend or how much power you run - IMO . . .