This page provides a chart with warp factor, speed, power requirements, etc.
In 2380, a team of Federation scientists and engineers (including Commander LaForge and Lieutenant Crusher) developed revolutionary new warp field configurations, calculations, and technology which have redefined Warp travel and necessitated a new warp scale.
The new scale is a more standard exponential equation with no theoretical limit, each warp factor being several times faster than the previous factor.
The standard warp scale seen in TNG, DS9, and VOY for the purposes of travel in RPGs is rediculously slow when compared to the size of the Federation. The Federation at it's greatest diameter is between 8,000 ly and 10,000 ly. If we were to assume a crusing speed of warp 8, it would take a ship a little less than 8 years to traverse federation space.
In "All Good Things" we saw Federation ships using an alternative warp scale, so there is prescedent.
Using this new scale, a cruising warp factor of 8 would take a starship about two years to travers the federation. In addition to the warp factor and relative speed, I've included the power requirements for use with the Star Trek Adventures RPG. Speeds with a power requirement of 0 are considered cruising speeds, do not cost additional energy to sustain, and do not generate significant wear-and-tear on the warp engines. According to Memory Alpha the time a ship could maintain maximum warp varied from days to months (Source).
In the Star Trek Adventures RPG, have the crew/ship perform skill checks probably (Engines + Engineering). Each sucess "buys" a challenge die. (May need to take into account ship / crew talents to augment this roll). Roll challenge dice equal to the number of sucesses. The rolled challenge dice score is the number days the ship may maintain maximus warp. Each effect counts as a month.