Try as we might, there is no rule of thumb for water cooling heat dissipation. The resultant capacity is heavily influenced by a variety of factor considerations including quasi-static intake air (sink) temperature and water temperature, radiator dynamics (size, thickness, fin density), flow rate, and fan speed, to include displacement and static pressure. Most values are empirically derived (i.e., tested) and not calculated.
The biggest impact to water temperature is, of course, thermal load. The loop water temperature will increase over time for a given thermal load as the air-to-water delta is driven higher, allowing for more heat rejection. Recall the rate of heat removal is a function of the difference in temperature between the temperature of the point of load and the cooling medium (temperature of intake air) for a given induction rate. The reason the water temperature increases is because this additional delta is necessary to create the condition necessary to balance heat in and heat out. Make sense?
Increasing either cooling medium (water) flow rate and/or fan speeds will reduce these deltas for a given load. Given the flow resistance of the loop for such small diameter passageways, increasing flow rate is difficult and typically reaches a point of diminishing returns well before additional airflow becomes a limiting factor.
Matching fan type (size and static pressure) is paramount when considering fin density for the radiator used. While higher fin densities typically provide additional heat rejection, this must be matched with a relatively high static fan pressure to be effective.
I would say 30C room temperature is OK but would recommend you get this down to at least 25C, if not lower.
A watercooling loop no-load to full-load delta of 10C or less is considered ideal. Systems above this limit are typically considered undersized and can be compensated by adding more radiator surface (and more fans) or simply increasing fan speed. At some point the fan noise becomes unbearable.
The other thing to consider is the increase in loop pressure. If you fill the loop with say, 20C water, seal it, and then drive it to 50C the change in pressure is going to be significant. Cycling this pressure has the potential to degrade the sealing capacity of the loop, usually at the connection points, leading to leaks over time. As well, higher water operating temperature will tend to increase losses to atmosphere but is less of a consideration for tubing of this type. Tygon will absolutely leach water over time at these temperatures at a fairly significant rate.
When I design a watercooling solution, I aim for no more than a 10C delta using fans at no more than 1500RPM. These considerations pretty much drive everything else. At full load, 50C water operating temperature makes me cringe. Keep this below 40C, preferably no more than 35C.
Hope this helps.
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