Setting axis label and histogram labels using GNUplot

I have the following GNUplot file:

set title "Performance of Quicksort over random data sets"
set yrange [0:80000]
set style data histogram
set style histogram cluster
set style fill solid border -1
set boxwidth 0.9
plot for [COL=2:6:1] 'timings.dat' using COL

and the following data file:

# Data-size being x-axis, each data size having a histogram-bar for seq/2-t/4-t/8-t/16-t (color-coded)
# Y-axis is time (the information in the columns below Sequential for example being the timings of sequential program for 2^15...2^28)

Data-size Sequential 2-threaded 4-threaded 8-threaded 16-threaded
2^15      6          4       5     7          10   
2^16      11         9       9     11         19   
2^17      24        17       18        24         32   
2^18      49        35       32        43         59   
2^19      102       71       70        89         115  
2^20      208       145      135       161        201  
2^21      431       295      281       333        416  
2^22      895       598      550       667        870  
2^23      1887      1219     1173      1228       1639 
2^24      3852      2979     2478      2621       3457 
2^25      7962      4980     4693      5064       6834 
2^26      16329     10151    9332      10062      13217
2^27      33775     21039    19072     20008      25196
2^28      69995     43393    38091     40598      52492

And this is what the resulting gnuplot image looks like:

My two issues are:

1. The x-axis should be labeled according to the data-size column (2^15,...,2^28)

2. The bars should be named according to their name in the data table (Sequential, 2-threaded, and so on)

I've read through parts of the manual, which got me to this stage, but I'm not experienced enough to understand how what I want can be done unfortunately.