As far as I know, the speed of light is constant relative to the observer. This means c2 will always be the same -- we can't change m = e / c2 to m = e / (something else).

The formula for relative mass is something like: m1 = m0 / sqrt(1 - v2/c2)
As v approaches c, v2 -> c2, (1 - v2/c2) -> 0, sqrt(0) = 0, m1 -> positive infinity (that is, approaches, but never reaches, because it would require an infinite amount of energy to accelerate an object to the speed of light, since its mass is increasing as it accelerates, so we never have to try divide by zero in this case).

"Time dilation" is similar -- t1 = t0 / sqrt(1 - v2/c2). So, like you said, time is not always equal -- it's not always experienced the same way from different observers. In fact it generally isn't as long as we're moving relative to each other, but at such a low speed the difference is impossible to tell.

Well, I just about exhausted my high-school relativity Goodnight!

Jibb