bought a Husky 455 Rancher last week, bought full chisel chain and ground the depth guides a wee bit down. It slices oak logs like butter, without pushing it in, just dropping it slowly. In heavy trees you NEVER have enough power, you'll allways be tempted to increase the cutting depth by grinding the depth gauges untill you run out of power. Power is NOT the deciding factor in buying a saw: The biggest drawback is weight. Husky sells the 140 (newly designed replacement of the 141 and 142 saws i used to have) as a basic saw, full plastic construction, will throw a chain when it gets hot and the plastic chain tensioner cover gets soft. Then you have the 240, slightly better, slightly more expensive. Then you have the 400 series which has better vibration isolators, better ergonomy, better longer lasting engines, and aluminium chain tensioner. And at last you have the 500 XP series which is the pro series.
Stihl, Husky are two main competing brands, just like Deere and Case. Stihl compares to Deere in terms of brand image, it has the strongest following and more agressive marketing, and as you can read in this thread, Stihl guys are louder in praising their saws than Husky guys (thats why i dont want a Stihl

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Stihl semi-pro saws offer clip-on covers (to get to the air filter and spark plug) where Husky only offers it on the pro series. Personally its no issue for me, because the spark plug socket has a screwdriver on the other end to tighten the chain and undo the top cover screws, you need that too with you anyways. I'm happy to trade those fast mount clips for some cash that stays in my pocket...
About your situation, 30 hours is enough to justify a semi-pro. If you do a lot of trimming and limbing, you're better off with a lighter saw. the 545 is of the pro series but isnt that much more expensive than the semipro series, and offers better power to weight ratio. the 445 is a good saw too, just a little cheaper but for similar performance you'd need to put a 450 against a 545. I would only go bigger to 50-55cc if you regularly cut trees whose diameter exceeds the length of a standard cutting bar, as only in those situations you can make use of the power, and the saw is on the wood instead of hanging on your arms most of the time.
Stihl off course has various hobby, semipro and pro models too, Jonsered is the same as Husky, and Dolmar seems to make good saws too (though ive never used one)