I've never been as heavy as the OP; at my peak I was pushing 220lbs. Still, I lost 50+ pounds by doing the following:
1) Keeping a food diary of every calorie that goes into my mouth. If I don't know how many calories something has, I don't eat it
2) Exercising 5-6 days a week for 45-60 minutes. For me, this typically means riding during my lunch hour. It kills two birds with one stone: not only am I burning calories on the bike, but I'm also not consuming a 1000+ calorie restaurant lunch. When I'm on the bike, I ride hard! It's just the way I'm wired: I can't go slow; my HR is always in the "aerobic zone" and I'm always trying to increase my average speed or beat my fastest time on a given route
3) Recording calories burned due to exercise. I have a PowerTap power meter that provides a relatively accurate estimate of calories burned while riding. Most of the HR monitors, websites, and apps that I've seen over-estimate calories burned while biking by 1.5-2X compared to what my power meter reports. The PT typically tells me I'm burning 500-550 calories/hr at an average pace of 16-18mph.
4) Eating more on days when I exercise. If my daily calorie budget is, say, 1500 calories and I burn 500 calories riding I'll eat an extra 350-400 calories (1500 - 500 + 400 = ~1400 calories "net"). If I feel super-hungry after a particular ride I might eat a little more. I don't worry if I'm a few hundred calories over my daily budget
5) Riding longer on weekends; typically 2-4 hours. These longer rides seem to be the ones that really accelerate weight loss for me. I slow my pace a bit for these longer rides (14-15mph rather than 16-18mph), but they're still pretty brisk. On rides that are 2+ hours in length, I consume 200-250 calories/hr. This food/drink gets recorded in my food log and deducted from my calorie budget
Keeping a food diary and trying to count calories has the side-effect of helping me make better food choices: fruits and veggies have fewer calories as compared to processed and packaged foods, which means you can eat a lot more of them and still stay within your calorie budget. My experience suggests that excess carbs are easily turned into fat, so I try to hit the 40/30/30 ratio of carbs/fat/protein, but I don't obsess about it.
The main target of this regimen is weight loss, but I find that it's still possible to build muscle, ride further, and climb longer while following it. I'm not going to suggest that your performance will increase as much as if you were eating more calories, merely that the two goals (weight loss, improved performance) aren't mutually exclusive.