I recommend splitting this climb up into two days. There is an alternative Boulder Creek approach that requires around 20 miles RT.
Round Trip 15 miles and 6,726-ft
Starting at the Pitkin Lake TH at 8,500-ft, locate the trail follow it 3.63 miles, passing two waterfalls en route. From here locate the drainage to the northeast that separates Peak V-“East Partner Peak” from “Vista Peak.” Leave the Pitkin Lake Trail and do an easy bushwhack up into the basin and continue another 1.36 miles to “Usable Pass” at 12,395-ft. This pass is just south of UN12,710-ft and it holds plenty of snow on its east side through July and into August. Bring an ax and crampons. From the pass, survey your terrain, and locate the obvious Peak Z-Prime and the not so obvious Peak Z, just northwest of Z-Prime. Both summits reside about 1.5 miles from the pass.
Descend “Usable Pass” into Upper Boulder Creek Basin and contour talus fields below Peak X’s southeast slopes. Peak X goes from here as well. Make your way into the lake riddled basin below Peak Z’s south slopes. Climb Peak Z’s south slopes to the summit- loose class 3.
For Z-Prime, descend Peak Z and hike to the start of Z-Prime's northwest ridge. Pick your way up to the ridge crest and ride it to the summit via exposed class 3 and 4 climbing. The rock here is bomberproof.
Maps and enough gear to survive a few days while rescue tries to locate you in the middle of nowhere.