You need to start doing some intervals where you hit your VO2 max. Typically, your HR serves as a proxy for VO2 - and if memory serves me right 95% of MHR is right around 100% VO2 max. To read more on this topic check out the articles at Peak Performance Online (with ideas for interval routines) and for a handy chart to translate HR into VO2 see the Sports Coach Home Page.
increases in VO2max, can be seen with a variety of intensities and volume, although to specifically target it you should ride at an intensity that elicits VO2max.
You'd not necessarily be that close using HR based training prescription, as it isn't overly useful for that type of training (the HR lag/response time can cloud your perception of intensity). A power meter is the best instrument for this.