Intake is always harder to fill, as the exhaust is under pressure and has very little trouble getting out. This is why intake valves are usually larger than exhaust valves. Typical SBC 4-barrel intake valves are 1.94 or 2.02, while the exhausts will only be 1.50 or 1.60.
When, how high, how fast, and for how long the intake valve stays open is probably the most important feature of a cam. If the intake valve opens too soon, the exhaust gasses can affect the incoming intake charge. If the intake valve opens too late, the cylinder will never have time to fill with the maximum air/fuel mixture possible. Once the intake valve starts to open, you want to open it fast and high to completely fill the cylinder. The hi-lift rocker arms (usually Barker or B&B) try to accomplish this by opening the intake valves a little more with the stock cam. Giving the exhaust valves extra lift wouldn't have as much effect as hi-lift on the intakes.
And yes, the hi-lift rockers can mess up the pushrod geometry on an engine. On SBC race car engines, we always checked pushrod geometry when using new cam or rocker arm profiles. We would mock-up a cylinder using light weight valve springs and rotate the engine to watch the pushrod contact angle change in it's seat in the rocker arm. By using an adjustable length pushrod made for such testing, you could play around to find the optimum pushrod length, and then buy or order pushrods made to that length.
